Effect of carbon nanotube incorporation on texture evolution and grain boundary constitution in NiCo coatings

Abstract

Corrosion response of NiCo-carbon nanotube (CNT) composite coatings is extremely sensitive to the CNT content and an optimum CNT amount yields highest corrosion resistance performance. Here, electron back scatter diffraction (EBSD) technique was employed to correlate the microstructure and corrosion behaviour of Ni–Co and NiCo-CNT composite coatings. Texture and grain boundary character distribution (GBCD) analysis revealed that for coating with the “optimum” CNT amount, factors like {111} orientation texture along [100] direction, high density of geometrically necessary dislocations (GNDs), high fraction of low angle grain boundaries (LAGBs) and Σ3 coincidence site lattice (CSLs) (coherent twins) are responsible for decelerated corrosion rate. Whereas, in pristine NiCo coating and NiCo coatings with high CNT content both of which show significantly higher corrosion rates, high energy orientation texture and high fraction of high energy grain boundaries like Σ3 CSLs (incoherent twins), asymmetrical tilt boundaries and high angle grain boundaries HAGBs increased corrosion rate.